Photo-detector filter having a cascaded low noise amplifier

ABSTRACT

Method and systems related to obstructing a first predefined portion of at least one defined wavelength of light incident upon a first photo-detector array; and detecting the at least one defined wavelength of light with a photo-detector in a second photo-detector array.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to, claims the earliest availableeffective filing date(s) from the following listed application(s) (the“Related Applications”) (e.g., claims earliest available priority datesfor other than provisional patent applications or claims benefits under35 USC § 119(e) for provisional patent applications), and incorporatesby reference in its entirety all subject matter of the following listedapplication(s) to the extent such subject matter is not inconsistentherewith; the present application also claims the earliest availableeffective filing date(s) from, and also incorporates by reference in itsentirety all subject matter of any and all parent, grandparent,great-grandparent, etc. applications of the “Related Application(s).

Related Applications

1. For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. NO. 10/744,057 entitled PHOTO-DETECTOR FILTER, namingW. Daniel Hillis, Roderick A. Hyde, Nathan P. Myhrvold, and Lowell L.Wood, Jr. as inventors, filed Dec. 22, 2003, which is currentlyco-pending, or is an application of which a currently co-pendingapplication is entitled to the benefit of the filing date.

2. For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. No. 10/742,517 entitled ANALOG-TO-DIGITAL CONVERTERCIRCUITRY, naming W. Daniel Hillis; Nathan P. Myhrvold, and Lowell L.Wood, Jr. as inventors, filed Dec. 19, 2003, which is currentlyco-pending, or is an application of which a currently co-pendingapplication is entitled to the benefit of the filing date.

3. For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. No. 11/598,208, entitled PHOTO-DETECTOR FILTER HAVING ACASCADED LOW NOISE AMPLIFIER, naming W. Daniel Hillis; Roderick A. Hyde;Nathan P. Myhrvold; Lowell L. Wood, Jr. as inventors, filed 9 Nov. 2006,which is currently co-pending, or is an application of which a currentlyco-pending application is entitled to the benefit of the filing date.

The United States Patent Office (USPTO) has published a notice to theeffect that the USPTO's computer programs require that patent applicantsreference both a serial number and indicate whether an application is acontinuation or continuation-in-part. Stephen G. Kunin, Benefit ofPrior-Filed Application, USPTO Official Gazette Mar. 18, 2003, availableat http;//www.uspto.gov/web/offices/com/sol/og/2003/week11/patbene.htm.The present Applicant Entity (hereinafter “Applicant”) has providedabove a specific reference to the application(s) from which priority isbeing claimed as recited by statute. Applicant understands that thestatute is unambiguous in its specific reference language and does notrequire either a serial number or any characterization, such as“continuation” or “continuation-in-part,” for claiming priority to U.S.patent applications. Notwithstanding the foregoing, Applicantunderstands that the USPTO's computer programs have certain data entryrequirements, and hence Applicant is designating the present applicationas a continuation-in-part of its parent applications as set forth above,but expressly points out that such designations are not to be construedin any way as any type of commentary and/or admission as to whether ornot the present application contains any new matter in addition to thematter of its parent application(s).

All subject matter of the Related Applications and of any and allparent, grandparent, great-grandparent, etc. applications of the RelatedApplications is incorporated herein by reference to the extent suchsubject matter is not inconsistent herewith.

TECHNICAL FIELD

The present application relates, in general, to photo-detector systems.

SUMMARY

In one aspect, a system includes but is not limited to: a firstphoto-detector array configured to obstruct a first predefined portionof at least one defined wavelength of light impinging upon said firstphoto-detector array; a second photo-detector array sensitive to the atleast one defined wavelength of light, said second photo-detector arraypositioned proximate to said first photo-detector array; and at leastone cascade of N gain elements operably couplable with at least one ofsaid first photo-detector array and said second photo-detector array,the at least one cascade having at least (i) N greater than or equal toa positive integer sufficient to provide said at least one cascade witha gain such that a predetermined operable signal at an input of said atleast one cascade generates a signal at an output of said at least onecascade that is larger than a predetermined operable threshold value,(ii) an input of a first gain element of said at least one cascadeoperably couplable with the at least one of said first photo-detectorarray and said second photo-detector array, and (iii) a gain element ofthe at least one cascade having a gain larger than one by an amount suchthat a noise factor of said at least one cascade operating on thepredetermined operable signal at the input of said at least one cascadeis substantially minimized. Other related system aspects are shown anddescribed elsewhere herein.

In one aspect, a method of constructing a system includes but is notlimited to: forming a first photo-detector array configured to obstructa first predefined portion of at least one defined wavelength of lightimpinging thereupon; forming a second photo-detector array sensitive tothe at least one defined wavelength of light in a vicinity of the firstphoto-detector array; configuring a first gain element such that aninput of the first gain element is operable to receive an input signalfrom at least one of the first photo-detector array and the secondphoto-detector array; connecting an output of a k'th gain element to aninput of a k+1'th gain element, wherein k is an integer that is at least1; configuring an N'th gain element of a cascade of N gain elements suchthat an output of the N'th gain element is operable to generate anoutput signal; and N being a positive integer such that a ratio betweenthe output signal and the input signal is larger than a predeterminedthreshold gain when the input signal is received at the input of thefirst gain element. Other related method aspects are shown and describedelsewhere herein.

In one aspect, a method of detecting light includes but is not limitedto: obstructing a first predefined portion of at least one definedwavelength of light incident upon a first photo-detector array;detecting the at least one defined wavelength of light with aphoto-detector in a second photo-detector array; and receiving at leastone signal representative of the least one defined wavelength of lightwith at least one cascade of N gain elements operably coupled with atleast one of the first photo-detector array and the secondphoto-detector array, the at least one cascade having at least (ii) Ngreater than or equal to a positive integer sufficient to provide saidat least one cascade with a gain such that a predetermined operablesignal at an input of said at least one cascade generates a signal at anoutput of said at least one cascade that is larger than a predeterminedoperable threshold value, (ii) an input of a first gain element of saidat least one cascade operably couplable with the at least one of thefirst photo-detector array and the second photo-detector array, and(iii) a gain element of the at least one cascade having a gain largerthan one by an amount such that a noise factor of said at least onecascade operating on the predetermined operable signal at the input ofsaid at least one cascade is substantially minimized. Other relatedmethod aspects are shown and described elsewhere herein.

In one or more various aspects, related systems include but are notlimited to circuitry and/or programming for effecting the method aspectsdescribed in the text and/or drawings of the present application; thecircuitry and/or programming can be virtually any combination ofhardware, software, and/or firmware configured to effect theforegoing-referenced method aspects depending upon the design choices ofthe system designer.

Various other method and or system aspects are set forth and describedin the text (e.g., claims and/or detailed description) and/or drawingsof the present application.

The foregoing is a summary and thus contains, by necessity;simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is NOT intended to be in any way limiting. Otheraspects, inventive features, and advantages of the devices and/orprocesses described herein, as defined solely by the claims, will becomeapparent in the non-limiting detailed description set forth herein.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows structure 100 that includes photo-detector arrays 102, 104,and 106.

FIG. 2 depicts system 200 that includes the subject matter shown in FIG.1.

FIG. 3 depicts system 200 that includes the subject matter shown in FIG.1.

FIG. 4 shows structure 400 that constitutes an alternate implementationof structure 100.

FIG. 5 depicts a partial view of system 500, which is similar to system200 of FIG. 2 except modified as shown and described herein.

FIG. 6 shows the structure of FIG. 5, modified to provideanalog-to-digital converters.

FIG. 7 illustrates a break out view of an alternate implementation oflower cascade 170 fed by bucket 110 as depicted in FIG. 6.

FIG. 8 shows an alternative embodiment of the structures of FIG. 6wherein the resistors have been replaced by capacitances.

FIG. 9 shows an alternative embodiment of the structures of FIG. 7wherein the resistors have been replaced by capacitances.

The use of the same symbols in different drawings typically indicatessimilar or identical items.

DETAILED DESCRIPTION

I. Photo-Detector Device(s) and/or Process(es)

With reference to the Figures, and with reference now to FIG. 1, shownis structure 100 that includes photo-detector arrays 102, 104, and 106.Example implementations of photo-detector arrays 102, 104, and 106include but are not limited to charge coupled device (CCD) sensorarrays, complementary metal oxide semiconductor (CMOS) sensor arrays,and/or mixtures of CCD and CMOS arrays. Those having skill in the artmay substitute other suitable types of photo-detector arrays in view ofthe teachings herein with a reasonable amount of experimentation.

Photon groups 107, 109, and 112 are depicted as respectively impingingupon photo-detectors 114, 116, and 118 of photo-detector array 102.Photo-detector array 102 is depicted as configured to obstruct apredefined portion of at least one defined wavelength of light impingingupon photo-detector array 102. As one specific example, photo-detectors114, 116, and 118 of photo-detector array 102 are illustrated asobstructing ½, or 50%, of the photons of photon groups 107, 109, and 112impinging upon photo-detector array 102. (While the examples herein areshown in terms of integral numbers of photons for clarity ofpresentation, those skilled in the art will recognize that otherrelative measures of brightness, intensity, power density, and/or otherproperties of light exist; specifically, those having skill in the artwill recognize that the response of specific devices may operate on asquare law format, straight linear format, or other format.) Thoseskilled in the art will recognize that the obstruction level of 50%discussed herein is illustrative only, and that different obstructionlevels are possible. Similarly, those skilled in the art will recognizethat the obstruction level may be chosen to be different in some or allof the specific photo-detectors.

Unobstructed portions 120, 122, and 124 of photon groups 107, 109, and112, respectively, are shown impinging upon photo-detectors 126, 128,and 130 of photo-detector array 104. Photo-detector array 104 isdepicted as configured to obstruct a predefined portion of at least onedefined wavelength of light impinging upon photo-detector array 104. Asone specific example, photo-detectors 126, 128, and 130 ofphoto-detector array 104 are illustrated as obstructing ½, or 50%, ofthe photons of portions 120, 122, and 124 of light impinging uponphoto-detector array 104.

Unobstructed portions 132, 134, and 136 of portions 120, 122, and 124,respectively, are shown impinging upon photo-detectors 138, 140, and 142of photo-detector array 106. Photo-detector array 106 is depicted asconfigured to obstruct a predefined portion of at least one definedwavelength of light impinging upon photo-detector detector array 106. Asone specific example, photo-detectors 138, 140, and 142 ofphoto-detector array 106 are illustrated as obstructing ½, or 50%, ofthe photons of portions 132, 134, and 136 impinging upon photo-detectorarray 106 (the single photon that would emerge from photo-detector 138is not shown for sake of clarity of presentation).

There are multiple advantages arising from structure 100. A few of theseadvantages will now be explicitly discussed in the context of processesshown and/or described in relation to FIGS. 2 and 3. For example,insofar as the predetermined portions obstructed and/or unobstructed byphoto-detector arrays 102, 104, and 106 are known, the array levels atwhich light is detected will allow strong inferences to be made as tothe intensity of photon groups 107, 109, and 112 respectively impingingupon photo-detectors 114, 116, and 118 of photo-detector array 102.Another advantage is that, insofar as photo-detector arrays 102, 104,and 106 are layered, the various layers may provide for more accuracy.Yet another advantage is that, insofar as photo-detector arrays 102,104, and 106 are layered, the various layers may extend the dynamicrange far beyond the saturation point of the photo-detectors in upperlevel photo-detectors, such as the photo-detectors in photo-detectorarray 102.

Referring now to FIG. 2, depicted is system 200 that includes thesubject matter shown in FIG. 1. System 200 may form an environment for aprocess that serves to illustrate a few of the advantages of structure100. As a specific example, shown following is that, in the event thatthe photo-detectors of photo-detector arrays 102, 104, and 106 are suchthat they saturate after the incidence of 6 photons, structure 100 willallow an image to be gathered that exceeds the saturation point of thephoto-detectors of uppermost photo-detector array 102. Specifically,although the photo-detectors saturate after 6 photons, the example ofFIG. 2 shows that intensity at photo-detector array 102 can be inferredbeyond the dynamic range of photo-detector array 102.

Charge detectors 238, 226, and 214 are shown as coupled to detect thecharge in photo-detectors 138, 126, and 114, respectively. Brightnessinference units 2380, 2260, and 2140 are shown as coupled to calculatethe intensity indicated by charge detectors 238, 226, and 214,respectively. Although only a few specific charge detector-brightnessinference unit combinations are shown and described herein, those havingskill in the art will recognize that, in most implementations, generallymost photo-detectors in use will be coupled to one or more similarcharge detector-brightness inference unit combinations, which willthereafter couple with one or more brightness inference selection units2500. Those having skill in the art will recognize that the teachingherein can be extended to virtually all suitable photo-detector arrays,including but not limited to Vertical, Linear, Interline, Full-frame,and Frame-transfer arrays via a reasonable amount of experimentation.The conventional aspects of such photo-detector architectures are notdescribed herein for sake of brevity.

Charge detector 238 is depicted as coupled to detect the charge inphoto-detector 138. Charge detector 238 is further shown as coupled tobrightness inference unit 2380. Brightness inference unit 2380 hasknowledge of photo-detector 106's relative place in the stack and thepredetermined light obstruction/unobstruction characteristics of thephoto-detectors in the stack above photo-detector 106. Accordingly,brightness inference unit 2380 can calculate a likely intensity ofphoton-group 107 impinging on uppermost photo-detector array 102. As aspecific example, the fact that photo-detector 126 of photo-detectorarray 104 is known to obstruct ½, or 50%, of its incidentphotons—coupled with the information from charge detector 238 that 2photons have impinged upon photo-detector 138—allows brightnessinference unit 2380 to calculate that approximately four photons wereincident upon photo-detector 126. Brightness inference unit 2380 canthereafter use this 4-photon inference coupled with the fact thatphoto-detector 114 of photo-detector array 102 is known to obstruct ½,or 50%, of its incident photons to calculate that approximately 8photons were incident upon photo-detector 114.

Charge detector 226 and brightness inference unit 2260 are depicted asworking in a fashion similar to charge detector 238 and brightnessinference unit 2380 to calculate that the 4 photons received byphoto-detector 126 indicate that approximately 8 photons were receivedby photo-detector 114.

Charge detector 214 and brightness inference unit 2140 are illustratedas working in a fashion similar to charge detector 238 and brightnessinference unit 2380 to calculate that the 8 photons received byphoto-detector 114 indicate that approximately 6 photons were receivedby photo-detector 114, since photo-detector 114—for sake of example—isassumed to saturate at 6 photons.

Brightness inference selection unit 2500 is shown as coupled to receivethe results of brightness inference units 2380, 2260, and 2140.Brightness inference selection unit 2500 runs various selection routinesto determine which of brightness inference units 2380, 2260, and 2140are likely most accurate. Continuing with the present example,brightness inference selection unit 2500 would note that brightnessinference unit 2140's calculation was at the threshold saturation pointof photo-detector 114, and would mark that calculation as suspect.Thereafter, brightness inference selection unit 2500 would note thatbrightness inference unit 2260's and 2380's calculations were above thethreshold saturation point of photo-detector 114. Consequently,brightness inference selection unit 2500 would average brightnessinference unit 2260's and 2380's calculations (ignoring brightnessinference unit 2140's at-threshold calculation) to get a brightnessinference of 8 photons.

Brightness inference selection unit 2500 is depicted as coupled toconventional display circuitry 2502. Conventional display circuitry 2502typically expects to receive one of a number of discrete signalsindicative of pixel brightness (what those signals are constitutes aconventional design choice). Continuing with the present example,brightness inference selection unit 2500 generates a signal indicativeof 8 photon brightness and delivers that signal over to conventionaldisplay circuitry 2502, which then uses the signal in a conventionalfashion to produce an image representation.

With reference now to FIG. 3, depicted is system 200 that includes thesubject matter shown in FIG. 1. System 200 may form an environment for aprocess that serves to illustrate of few of the advantages of structure100. As a specific example, shown following is that, in the event thatphoton group 109 is such that there is “quantization error” introducedby the filtering photo-detectors, the fact that there are multiplelayers of filters allows system 200 to increase the likelihood that such“quantization errors” can be corrected.

Charge detector 340 is depicted as coupled to detect the charge inphoto-detector 140. Charge detector 340 is further shown as coupled tobrightness inference unit 3400. Brightness inference unit 3400 hasknowledge of photo-detector array 106's (e.g., photo-detector 140's)relative place in the stack and the predetermined lightobstruction/unobstruction characteristics of the photo-detectors in thestack above photo-detector array 106 (photo-detector 140). Accordingly,brightness inference unit 3400 can calculate a likely intensity ofphoton-group 109 impinging on uppermost photo-detector array 102. As aspecific example, the fact that photo-detector 128 of photo-detectorarray 104 is known to obstruct ½, or 50%, of its incidentphotons—coupled with the information from charge detector 340 that 1photon has impinged upon photo-detector 140—allows brightness inferenceunit 3400 to calculate that approximately 2 photons were incident uponphoto-detector 128; unfortunately, since the 1 photon impinging uponphoto-detector 140 is the result of photo-detector 128 filtering 50% of3 photons, there is quantization error in the filtering which makes thiscalculated intensity of the light at photo-detector array 104 lessaccurate than without the quantization error. Brightness inference unit3400 can thereafter use this 2-photon inference coupled with the factthat photo-detector 116 of photo-detector array 102 is known to obstruct½, or 50%, of its incident photons to calculate that approximately 4photons were incident upon photo-detector 116.

Charge detector 328 and brightness inference unit 3280 are depicted asworking in a fashion similar to charge detector 340 and brightnessinference unit 3400. Brightness inference unit 3280 has knowledge ofphoto-detector array 104's (e.g., photo-detector 128's) relative placein the stack and the predetermined light obstruction/unobstructioncharacteristics of the photo-detector in the stack above photo-detector104 (e.g., photo-detector 128). Accordingly, brightness inference unit3280 can calculate a likely intensity of photon-group 109 impinging onuppermost photo-detector array 102. Continuing with the present example,the fact that photo-detector 116 of photo-detector array 102 is known toobstruct ½, or 50%, of the photons, coupled with the information fromcharge detector 328 that 3 photons have impinged upon photo-detector 128allows brightness inference unit 3280 to calculate that approximately 6photons were incident upon photo-detector 116. Brightness inference unit3280 can thereafter use this 6-photon inference coupled with the factthat photo-detector 116 of photo-detector array 102 is known to obstruct½, or 50%, of the photons to calculate that approximately 6 photons wereincident upon photo-detector 116.

Charge detector 316 and brightness inference unit 3160 are illustratedas working in a fashion similar to charge detector 340 and brightnessinference unit 3400 to calculate that the 6 photons received byphoto-detector 116 indicate that approximately 6 photons were receivedby photo-detector 116.

Brightness inference selection unit 2500 is shown as coupled to receivethe results of brightness inference units 3400, 3280, and 3160.Brightness inference selection unit 2500 runs various selection routinesto determine which of brightness inference units 3400, 3280, and 3160are likely most accurate. Continuing with the present example,brightness inference selection unit 2500 would note that brightnessinference unit 3160's calculation was at the threshold saturation pointof photo-detector 114, and would mark that calculation as suspect.Thereafter, brightness inference selection unit 2500 would note thatbrightness inference unit 3280's and 3400's calculations do not agree.Consequently, brightness inference selection unit 2500 would detect thatbrightness inference unit 3280's calculation matched brightnessinference unit 3160's calculation, even though brightness inference unit3160's calculation shows a threshold saturation value; accordingly,brightness inference selection unit would treat brightness inferenceunit 3160's calculation as accurate and then average all threecalculations of brightness inference units 3400, 3280, and 3160 (e.g.,(4+6+6)/3=5.33) to select a brightness inference of 6 photons as mostlikely; alternatively, the fact that brightness inference unit 3280makes its threshold inference based on more collected charge (e.g., asindicated by charge detector 328) than the charge collected by lowermostbrightness inference unit 3400 could be used to decide that brightnessinference unit 3280's calculation was the more accurate. Those havingskill in the art will appreciate other selection routines in light ofthe teachings herein.

Photo-detector arrays 102, 104, 106 have been described herein asconfigured to obstruct predefined portions of at least one definedwavelength of light impinging upon photo-detector arrays 102, 104, 106.There are many different ways in which such photo-detector arrays may beimplemented. In some implementations of the photo-detector arrays, atleast one photo-detector is constructed to provide an optical filterhaving a passband including at least one of a red, a blue, and a greenvisible light wavelength. Exemplary implementations includephoto-detectors constructed to filter red, blue, and green visible lightwavelengths either individually or in some combination thereof. Otherexemplary implementations include photo-detectors constructed to filter400 through 800 nm wavelengths of light either individually or in somecombination thereof.

In other implementations of the photo-detector arrays, at least onephoto-detector is constructed to provide a substantially neutral densityfilter (neutral density filters attenuate incident light withoutsignificantly altering its spectral distribution over a defined group ofwavelengths of interest). In one exemplary implementation, one or morephoto-detectors are constructed to provide a neutral density filter thatdecreases an intensity of light energy without substantially altering arelative spectral distribution of an unobstructed portion of the lightenergy. In another exemplary implementation, one or more photo-detectorsare constructed to provide a substantially neutral density filter thatfilters an entire visible spectrum substantially evenly withoutsubstantially influencing at least one of color and contrast of anunobstructed portion of the entire visible spectrum. In anotherexemplary implementation, one or more photo-detectors are constructed toprovide a substantially neutral density filter that utilizes at leastone of absorption and reflection. In another exemplary implementation,one or more photo-detectors are constructed to provide a substantiallyneutral density filter that filters substantially ½ of the lightimpinging upon the photo-detectors. In another exemplary implementation,one or more photo-detectors are constructed to provide a substantiallyneutral density filter that filters a defined portion of photons atleast partially composing the light impinging upon said firstphoto-detector. The examples herein are not intended to be exhaustive,and those having skill in the art may substitute other types ofphoto-detector arrays in view of the teachings herein with a reasonableamount of experimentation.

Referring now to FIG. 4, shown is structure 400 that constitutes analternate implementation of structure 100. Spectrally dependent filter402 is depicted interposed between photo-detector array 102 andphoto-detector array 104. Those skilled in the art will recognize thatspectrally-dependent filter 402 can be either monolithic (as shown inFIG. 4), or can be spatially differentiated using either the samepixilation pattern as in photo-detector arrays 102 or 104, or using adifferent pattern. Although only two photo-detector arrays and onespectrally-dependent filter are shown in FIG. 4, structure 400 isintended to be representative of its shown components repeated manytimes, and is also intended to be representative of a composite ofstructures 100 of FIG. 1 and structure 400 of FIG. 4. In addition,although not explicitly shown, it will be appreciated by those havingskill in the art that FIGS. 2 and 3 can be modified to include andutilize the subject matter of FIG. 4 with a routine amount ofexperimentation.

In one implementation, spectrally dependent filter 402 can be depictedinterposed between photo-detector array 102 and photo-detector array104. Spectrally dependent filter 402 is used to equalize the filteringof photo-detector array 102 so that the various wavelengths of portions120, 122, and 124 have been like filtered prior to impinging uponphoto-detector 104. For example, in some implementations, photo-detectorarray 102 will not provide a true neutral density filter function acrossred, blue, and green wavelength light. Specifically, assume thatphoto-detector array 102 allowed 50% of the red and blue light to passbut allowed 60% of the green light to pass. In such a situation,spectrally-dependent filter 402 would provide an additional green filterso that the red, blue, and green light were all filtered approximately50% when they reached photo-detector 104.

In another implementation, spectrally dependent filter 402 can bedesigned to attenuate at least one first wavelength (e.g., blue light)substantially more than at least one second wavelength (e.g., redlight). In such a situation, the difference between signals detected byphoto-detector array 104 and photo-detector array 102, can be used todetermine the spectral composition of light impinging upon structure400.

In another example implementation of spectrally-dependent filter 402,spectrally-dependent filter 402 is constructed to filter at least onedefined wavelength of light between about 400 and about 800 nano-meters.

In one example implementation of structure 400, photo-detector arraysproximate to each other are constructed of different semi-conductormaterials.

In another example implementation of structure 400, spectrally-dependentfilter 402 is made from a semi-conductor material that is the same asthe material used in at least one of the first and second photo-detectorarrays, the semiconductor material having at least one of a dopingmaterial and a concentration chosen to meet a predefined amount ofoptical obstruction; in an alternate implementation, the material isdifferent from that of a photo-detector array proximate tospectrally-dependent filter 402.

In another example implementation of structure 400, spectrally-dependentfilter 402 provides its filtering/obstruction properties via at leastone of absorption and reflection mechanisms.

In another example implementation of structure 400, spectrally-dependentfilter 402 provides an amount of obstruction substantially different forat least one second defined wavelength of light than for the at leastone defined wavelength of light which photo-detector array 102 has beenconfigured to obstruct.

In another example implementation of structure 400, spectrally-dependentfilter 402 provides an amount of obstruction substantially the same fora defined set of wavelengths, the set containing the first definedwavelength of light.

In another example implementation of structure 400, at least onephoto-detector in a photo-detector array substantially matches at leastone of the size, shape, and lateral location of at least onephoto-detector in another photo-detector array.

In another example implementation of structure 400, at least onephoto-detector in one photo-detector array is in respective substantialalignment with a plurality of photodetectors in another photo-detectorarray.

In another example implementation of structure 400, the photo-detectorarrays are each permeable to a first and a second defined wavelength oflight.

In another example implementation of structure 400, structure 400contains a set of N+1 photo-detector arrays, each pair of which isproximate to and separated by an optical filter, such that relativeoptical spectrums entering N of the photo-detector arrays aresubstantially different from each other, and such that a relativeoptical spectrum entering photo-detector array N+1 has a substantiallysimilar relative spectrum as that relative spectrum entering the firstphoto-detector array.

II. Amplification and/or Conversion Device(s) and/or Process(es)

With reference now to FIG. 5, depicted is a partial view of system 500,which is similar to system 200 of FIG. 2 except modified as shown anddescribed herein. Cascades of N gain elements are shown respectivelyinterposed between charge detectors 214, 226, and 238 andphoto-detectors 114, 126, and 138. Although only three chargedetector-photo-detector pairings are explicitly described herein, it isto be understood that in typical applications an appreciable portion ofrespectively paired charge detectors and photo-detectors will havecascades of similarly interposed gain elements.

Photo-detector arrays 102, 104, and 106 are illustrated as havingindividual photodetectors arranged in a row and column format. Thosehaving skill in the art will appreciate that photo-detector arrays 102,104, and 106 are meant to be inclusive of substantially all suitablephoto-detector arrays, including but not limited to Vertical, Linear,Interline, Full-frame, and Frame-transfer arrays.

As noted above, charge detectors 214, 226, and 238 detect the aggregatecharges of their respectively connected photo-detectors 114, 126, and138. Each individual photo-detector 114, 126, and 138 typically collectscharges generated by incident photons over a defined interval (e.g., anexposure time interval). As a shorthand notation used for ease ofunderstanding, each photo-detector is described herein as collecting“buckets” of charge Q, where the buckets of charge are representative oflight received during an interval. While examples are set forth hereinin terms of charge buckets emerging from photo-detector arrays 102, 104,and 106, those having skill in the art will appreciate that theteachings herein may be applied to voltage and/or current-basedconfigurations with a minor amount of experimentation. For example, theteachings herein may be applied to systems that include microphones,temperature detectors, thermocouples, etc. with minor amounts ofexperimentation.

Different buckets 108 and 110 of aggregate charge QA and QB areillustrated as having been generated by photo-detectors 114 and 138where each bucket 108 and 110 represents the aggregate charge “Q”respectively collected by photo-detectors 114 and 138 over some periodof time (e.g., an exposure time). The fact that each bucket 108, 110contains an aggregate charge collected over time is depicted by thelowercase “q”s making up the uppercase “QA” and “QB” in buckets 108 and110. Buckets 108 and 110 will typically contain different amounts ofcharge.

Buckets 108 and 110, with aggregate charges QA and QB, are shown asoutputs of photo-detectors 114 and 138 applied to inputs of therespective cascades 150, 170 of k=1 to N gain elements. Althoughcascades 150 and 170 are each shown having N gain elements, such is notrequired. For instance, cascade 150 could have k=1 to J elements, whereJ is a different number than N.

Focusing now on cascade 170, the number N is preferably chosen to begreater than or equal to a positive integer sufficient to providecascade 170 with a gain such that a predetermined operable signal at aninput of cascade 170 generates a signal at an output of cascade 170 thatis larger than a predetermined operable threshold value. In oneimplementation, this is achieved by choosing N such that when an outputof photo-detector 138 is at or near the lower end of photo-detector138's operable range the overall gain of cascade 170 will be largeenough to provide charge detector 238 with a signal at or above chargedetector 238's operable range lower end.

In one implementation, the gain elements of cascade 170 preferably havea gain larger than one by an amount such that the noise factor ofcascade 170 operating on the predetermined signal at the input of the atleast one cascade 170 is substantially minimized (e.g., having a noisefactor at or near one, such as a noise factor less than 1.1 or 1.2).There are various ways in which the noise factor may be viewed. Forinstance, the noise factor may be viewed as the ratio of a Signal Powerto Thermal Noise ratio at the input of the at least one cascade to anamplified Signal Power to Thermal Noise ratio at the output of the atleast one cascade: (S_(input)/N_(input))/(S_(output)/N_(output)).Alternatively, the noise factor may be viewed as a ratio of an outputnoise power of the at least one cascade to the portion thereofattributable to thermal noise in an input termination at standard noisetemperature. Alternatively again, the noise factor may be viewed as aratio of actual output noise to that which would remain if the at leastone cascade itself did not introduce noise. In one implementation, thegains of the gain elements in cascade 170 are chosen larger than one byan amount that is practicably small such that the noise contribution tothe low noise amplifier from a gain element is substantially minimized.In one implementation, the N gain elements are preferably chosen to bevery low gain amplifiers (e.g., gains greater than 1.00 (one) but lessthan 1.01 (one point zero one) or 1.001 (one point zero zero one) thatproduce very little additive noise. One example of such extremely lowgain amplifiers that produce little additive noise are slightlyover-biased amplifiers.

In one implementation, the N gain elements are preferably chosen toinclude one or more impact ionization-based amplifiers, such as thoseused in the Texas Instruments IMPACTRON CCDs (available from TexasInstruments Inc., Richardson, Tex., USA) or those used in the MarconiL3Vision CCDs (available from Marconi Applied Technology, UnitedKingdom). Such amplifiers can use a signal-boosting technique that mayeffectively reduce CCD read-out noise by a gain factor.Impact-ionization based amplifiers preferably use special high-voltageclocking which can both initiate and then sustain an impact ionizationprocess. When cascade 170 is implemented with such technologies, bucket110 of charge can be multiplied such that greatly improvedsignal-to-noise ratio for signal levels in the vicinity of thephoto-detector 138 read-noise floor may be achieved. In anotherimplementation, the N gain elements are preferably chosen to include oneor more low noise operational amplifiers.

With reference now to FIG. 6, shown is the structure of FIG. 5, modifiedto provide analog-to-digital converters. Cascade 150 fed by bucket 108of aggregate charge QA is shown having P attached voltage comparators.The inputs of gain elements having the attached comparators are alsoshown as having resistors connected to ground. These resistors arepreferably large so as to draw as little current as is practicable. Eachcomparator is illustrated as having its own respective reference voltagedepicted as reference voltage_1 through reference voltage_P. Therespective comparators trigger when the voltages across their respectiveresistors exceed their respective reference voltages. In anotherembodiment (not shown) current comparators are used to directly sensethe current.

Each comparator 1-P is depicted as having an output to charge detector214. Charge detector 214 is shown as using the quantized output of thevarious comparators 1-P to augment the amplified value received fromcascade 150 of gain elements. In one implementation, the comparators 1-Pare such that charge detector 214 may use the quantized output toprovide a direct quantization and/or digital conversion; these alternateimplementations are depicted in FIG. 6 by the dashed line connecting theNth gain element with charge detector 214, and are also shown anddescribed further herein.

Cascade 170 fed by bucket 110 of aggregate charge QB is shown having Mattached comparators. The inputs of gain elements having the attachedcomparators are also shown as having resistors connected to ground.These resistors are preferably large so as to draw as little current asis practicable. Each comparator is illustrated as having its ownrespective reference voltage depicted as reference voltage_1 throughreference voltage_M. The respective comparators will trigger when thevoltages across their respective resistors exceed their respectivereference voltages. In another embodiment (not shown) currentcomparators are used to directly sense the current.

Each comparator 1-M is depicted as having an output to charge detector238. Charge detector 238 is shown as using the quantized output of thevarious comparators 1-M to augment the amplified value received fromcascade 170 of gain elements. In one implementation, the comparators 1-Mare such that charge detector 238 may use the quantized output toprovide a direct quantization and/or digital conversion; these alternateimplementations are depicted in FIG. 6 by the dashed line connecting theNth gain element with charge detector 238, and are also shown anddescribed further herein.

Continuing to refer to FIG. 6, and concentrating on cascade 170 fed bybucket 110, notice that since the N gain elements are cascaded, thesignal will be less amplified near the first gain element and moreamplified near the Nth gain element. Accordingly, if the referencevoltages 1-M were all set to have the same value, and each of the N gainelements had about the same gain values, the comparator that triggeredclosest to the 1^(st) gain element would be indicative of the amount ofcharge, QB, input to cascade 170. For example, for some input bucket 110of charge, if the second comparator, with reference voltage_2,triggered, but the first comparator with reference voltage_1 did not,the known gains of the stages could be used to infer the amount ofcharge QB. That is, it would be known that (a) QB×Gain of Element1<ReferenceVoltage_1; and that (b) QB×(Gain of Element 1×Gain of Element2×Gain of Element 3×Gain of Element 4)>Reference Voltage_2.Specifically, with both reference voltage_1 and reference voltage_2arbitrarily chosen to have a value of 2, and the gains of the first,second, third, and fourth elements all arbitrarily chosen as 1.01, thescheme would yield: QB×1.01<2=QB<1.98; andQB×(1.01×1.01×1.01×1.01)>2=QB>1.92. Thus, the structure indicates that1.92<QB<1.98. Thereafter, QB can be further quantized and/or digitizedby charge detector 238 using conventional techniques. In otherembodiments the comparators and resistors can be distributed for yetmore precision (e.g., 1 for every gain element). In yet otherembodiments, the comparators and resistors can be distributed and thevoltage reference levels manipulated in light of specified discretechanges in the amount of charge QB, thereby allowing the output of thecomparators to function as direct digital output values.

Referring now to FIG. 7, illustrated is a break out view of an alternateimplementation of lower cascade 170 fed by bucket 110 as depicted inFIG. 6. Specifically, each of the resistors and comparators 1-M areshown respectively connected every 3^(rd) gain element. Comparators 1-Mare depicted as connected to charge detector 238, while gain element Nis shown as not connected to charge detector 238.

Assuming that the gain elements all have roughly the same gain, in thisimplementation, charge detector 238 may directly use the comparatoroutputs to get direct digital conversion of the analog charge Q2 ofbucket 110.

With reference now to FIG. 8, shown is an alternative embodiment of thestructures of FIG. 6 wherein the resistors have been replaced bycapacitances. One implementation in which the structures of FIG. 8 proveuseful is that wherein the time interval between successive buckets ofcharge clocked into cascade 170 of N gain elements is greater than thetime needed for cascade 170 to effectively settle. That is, in a circuitwhere cascade 170 responds so fast that cascade 170 will haveeffectively completed its response to bucket 110 of charge QB longbefore a next bucket of charge is shifted onto the input of cascade 170.As cascade 170 settles in response to bucket 100 of charge QB, thecapacitors associated with the respective comparators 1-M will gathercharge and present voltage which can be monitored in a fashion analogousto that described above in relation to FIG. 6. The remaining componentsof FIG. 8 function analogous to like components described elsewhereherein.

With reference now to FIG. 9, shown is an alternative embodiment of thestructures of FIG. 7 wherein the resistors have been replaced bycapacitances. The structures of FIG. 9 prove particularly useful ininstances similar to those described in relation to FIG. 8. Thecomponents of FIG. 9 function analogous to like components describedelsewhere herein.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and examples. Insofar as such block diagrams, flowcharts, and examplescontain one or more functions and/or operations, it will be understoodas notorious by those within the art that each function and/or operationwithin such block diagrams, flowcharts, or examples can be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof. In one embodiment, thepresent invention may be implemented via Application Specific IntegratedCircuits (ASICs), Field Programmable Gate Arrays (FPGAs), or otherintegrated formats. However, those skilled in the art will recognizethat the embodiments disclosed herein, in whole or in part, can beequivalently implemented in standard integrated circuits, as one or morecomputer programs running on one or more computers (e.g., as one or moreprograms running on one or more computer systems), as one or moreprograms running on one or more processors (e.g., as one or moreprograms running on one or more microprocessors), as firmware, or asvirtually any combination thereof, and that designing the circuitryand/or writing the code for the software and or firmware would be wellwithin the skill of one skilled in the art in light of this disclosure.In addition, those skilled in the art will appreciate that themechanisms of the present invention are capable of being distributed asa program product in a variety of forms, and that an illustrativeembodiment of the present invention applies equally regardless of theparticular type of signal bearing media used to actually carry out thedistribution. Examples of a signal bearing media include, but are notlimited to, the following: recordable type media such as floppy disks,hard disk drives, CD ROMs, digital tape, and computer memory; andtransmission type media such as digital and analog communication linksusing TDM or IP based communication links (e.g., packet links).

In a general sense, those skilled in the art will recognize that thevarious embodiments described herein which can be implemented,individually and/or collectively, by various types of electro-mechanicalsystems having a wide range of hardware, software, firmware, orvirtually any combination thereof. Consequently, as used herein“electro-mechanical system” includes, but is not limited to, electricalcircuitry operably coupled with a transducer (e.g., an actuator, amotor, a piezoelectric crystal, etc.), electrical circuitry having atleast one discrete electrical circuit, electrical circuitry having atleast one integrated circuit, electrical circuitry having at least oneapplication specific integrated circuit, electrical circuitry forming ageneral purpose computing device configured by a computer program (e.g.,a general purpose computer configured by a computer program which atleast partially carries out processes and/or devices described herein,or a microprocessor configured by a computer program which at leastpartially carries out processes and/or devices described herein),electrical circuitry forming a memory device (e.g., forms of randomaccess memory), electrical circuitry forming a communications device(e.g., a modem, communications switch, or optical-electrical equipment),and any non-electrical analog thereto, such as optical or other analogs.

Those skilled in the art will recognize that it is common within the artto describe devices and/or processes in the fashion set forth herein,and thereafter use standard engineering practices to integrate suchdescribed devices and/or processes into image processing systems. Thatis, at least a portion of the devices and/or processes described hereincan be integrated into an image processing system via a reasonableamount of experimentation. Those having skill in the art will recognizethat a typical image processing system generally includes one or more ofa system housing unit, a video display device, a memory such as volatileand non-volatile memory, processors such as microprocessors and digitalsignal processors, computational entities such as operating systems,drivers, and applications programs, one or more interaction devices,such as a touch pad or screen, control systems including feedback loopsand control motors (e.g., feedback for sensing lens position and/orvelocity; control motors for moving/distorting lenses to give desiredfocuses. A typical image processing system may be implemented utilizingany suitable commercially available components, such as those typicallyfound in digital still systems and/or digital motion systems.

The foregoing described embodiments depict different componentscontained within, or connected with, different other components. It isto be understood that such depicted architectures are merely exemplary,and that in fact many other architectures can be implemented whichachieve the same functionality. In a conceptual sense, any arrangementof components to achieve the same functionality is effectively“associated” such that the desired functionality is achieved. Hence, anytwo components herein combined to achieve a particular functionality canbe seen as “associated with” each other such that the desiredfunctionality is achieved, irrespective of architectures or intermedialcomponents. Likewise, any two components so associated can also beviewed as being “operably connected” or “operably coupled” to each otherto achieve the desired functionality.

While particular embodiments of the present invention have been shownand described, it will be understood by those skilled in the art that,based upon the teachings herein, changes and modifications may be madewithout departing from this invention and its broader aspects and,therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. Furthermore, it is to be understood that theinvention is solely defined by the appended claims. It will beunderstood by those within the art that, in general, terms used herein,and especially in the appended claims (e.g., bodies of the appendedclaims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”“comprise” and variations thereof, such as, “comprises” and “comprising”are to be construed in an open, inclusive sense, that is as “including,but not limited to,” etc.). It will be further understood by thosewithin the art that if a specific number of an introduced claimrecitation is intended, such an intent will be explicitly recited in theclaim, and in the absence of such recitation no such intent is present.For example, as an aid to understanding, the following appended claimsmay contain usage of the introductory phrases “at least one” and “one ormore” to introduce claim recitations. However, the use of such phrasesshould NOT be construed to imply that the introduction of a claimrecitation by the indefinite articles “a” or “an” limits any particularclaim containing such introduced claim recitation to inventionscontaining only one such recitation, even when the same claim includesthe introductory phrases “one or more” or “at least one” and indefinitearticles such as “a” or “an” (e.g., “a” and/or “an” should typically beinterpreted to mean “at least one” or “one or more”); the same holdstrue for the use of definite articles used to introduce claimrecitations. In addition, even if a specific number of an introducedclaim recitation is explicitly recited, those skilled in the art willrecognize that such recitation should typically be interpreted to meanat least the recited number (e.g., the bare recitation of “tworecitations,” without other modifiers, typically means at least tworecitations, or two or more recitations).

1. A method of detecting light comprising: receiving at least one signalwith at least one cascade of N gain elements operably couplable withcircuitry, the at least one cascade having at least: N greater than orequal to a positive integer sufficient to provide the at least onecascade with a gain such that a predetermined operable signal at aninput of the at least one cascade generates a signal at an output of theat least one cascade that is larger than a predetermined operablethreshold value; an input of a gain element of the at least one cascadeoperably couplable with the circuitry; a gain element of the at leastone cascade having a gain larger than one by an amount such that a noisefactor of said the at least one cascade operating on the predeterminedoperable signal at the input of the at least one cascade issubstantially minimized; and one or more output value detection circuitsrespectively operably coupled with one or more outputs of the N gainelements.
 2. The method of claim 1, wherein said receiving at least onesignal comprises: receiving the at least one signal from aphoto-detector array.
 3. The method of claim 2, wherein said receivingthe at least one signal from a photo-detector array comprises: receivingthe at least one signal from at least one of a charge coupled device(CCD) array or a complementary metal oxide semiconductor (CMOS) array.4. The method of claim 1, wherein the N greater than or equal to apositive integer sufficient to provide the at least one cascade with again such that a predetermined operable signal at an input of the atleast one cascade generates a signal at an output of the at least onecascade that is larger than a predetermined operable threshold valuefurther comprises: the N greater than or equal to a positive integersufficient to provide the at least one cascade with a gain such that asubstantially minimally rated output signal of a photo-detector arrayapplied to the input of the at least one cascade generates a signal atthe output of the at least one cascade that is larger than thepredetermined operable threshold value.
 5. The method of claim 1,wherein the N greater than or equal to a positive integer sufficient toprovide the at least one cascade with a gain such that a predeterminedoperable signal at an input of the at least one cascade generates asignal at an output of the at least one cascade that is larger than apredetermined operable threshold value further comprises: the N isgreater than or equal to a positive integer sufficient to provide the atleast one cascade with a gain such that a predetermined signal at aninput of the at least one cascade generates a signal at the output ofthe at least one cascade that is larger than a substantially minimallyrated input of a display circuit.
 6. The method of claim 1, wherein thegain element of the at least one cascade having a gain larger than oneby an amount such that a noise factor of the at least one cascadeoperating on the predetermined operable signal at the input of the atleast one cascade is substantially minimized further comprises: a noisefactor defined as a ratio of a Signal Power to Thermal Noise ratio atthe input of the at least one cascade to an amplified Signal Power toThermal Noise ratio at the output of the at least one cascade:(S_(input)/N_(input))/(S_(output)/N_(output)).
 7. The method of claim 1,wherein the gain element of the at least one cascade having a gainlarger than one by an amount such that a noise factor of the at leastone cascade operating on the predetermined operable signal at the inputof the at least one cascade is substantially minimized furthercomprises: a noise factor defined as a ratio of an output noise power ofthe at least one cascade to the portion thereof attributable to thermalnoise in an input termination at standard noise temperature.
 8. Themethod of claim 1, wherein the gain element of the at least one cascadehaving a gain larger than one by an amount such that a noise factor ofthe at least one cascade operating on the predetermined operable signalat the input of the at least one cascade is substantially minimizedfurther comprises: a noise factor defined as a ratio of actual outputnoise to that which would remain if the at least one cascade itself didnot introduce noise.
 9. The method of claim 1, wherein the gain elementof the at least one cascade having a gain larger than one by an amountsuch that a noise factor of the at least one cascade operating on thepredetermined operable signal at the input of the at least one cascadeis substantially minimized further comprises: the gain larger than onebut less than 1.001.
 10. The method of claim 1, wherein the gain elementof The at least one cascade having a gain larger than one by an amountsuch that a noise factor of the at least one cascade operating on thepredetermined operable signal at the input of the at least one cascadeis substantially minimized further comprises: the gain larger than onebut less than 1.01.
 11. The method of claim 1, wherein the gain elementof the at least one cascade having a gain larger than one by an amountsuch that a noise factor of the at least one cascade operating on thepredetermined operable signal at the input of the at least one cascadeis substantially minimized further comprises: the gain of a gain elementis larger than one by an amount that is practicably small such that thenoise contribution to the low noise amplifier from a gain element issubstantially minimized.
 12. The method of claim 1, wherein the gainelement of the at least one cascade having a gain larger than one by anamount such that a noise factor of the at least one cascade operating onthe predetermined operable signal at the input of the at least onecascade is substantially minimized further comprises: an impactionization-based amplifier having a gain larger than one by an amountsuch that the noise factor of the at least one cascade operating on thepredetermined operable signal at the input of the cascade issubstantially minimized.
 13. The method of claim 1, further comprising:detecting that a first gain element output of N gain elements in acascade is below a first predefined threshold; and determining a digitalconversion value in response to a detection that a second gain elementoutput of the N gain elements in the cascade is above a secondpredefined threshold greater than the first predefined threshold. 14.The method of claim 13, wherein said determining a digital conversionvalue in response to a detection that a second gain element output ofthe N gain elements in the cascade is above a second predefinedthreshold greater than the first predefined threshold comprises:obtaining a first bound by dividing the first predefined threshold by anaggregate gain between the first gain element output and a definedanalog input; obtaining a second bound by dividing the second predefinedthreshold by an aggregate gain between the second gain element outputand the defined analog input; determining a signal value bounded by thefirst bound and the second bound; and obtaining the digital conversionvalue in response to the signal value.
 15. The method of claim 14,wherein said obtaining the digital conversion value in response to thesignal value comprises: designating the signal value as the digitalconversion value.
 16. The method of claim 14, wherein said obtaining thedigital conversion value in response to the signal value comprises: atleast one of quantizing the signal value or digitizing the signal value.17. The method of claim 13, wherein said determining a digitalconversion value in response to a detection that a second gain elementoutput of the N gain elements in the cascade is above a secondpredefined threshold greater than the first predefined thresholdcomprises: receiving one or more output signals of the N gain elementswith one or more comparators respectively operably coupled with the oneor more outputs of the N gain elements.
 18. A system of detecting lightcomprising: means for receiving at least one signal with at least onecascade of N gain elements operably couplable with circuitry, the atleast one cascade having at least: N greater than or equal to a positiveinteger sufficient to provide the at least one cascade with a gain suchthat a predetermined operable signal at an input of the at least onecascade generates a signal at an output of the at least one cascade thatis larger than a predetermined operable threshold value; an input of again element of the at least one cascade operably couplable with thecircuitry; a gain element of the at least one cascade having a gainlarger than one by an amount such that a noise factor of the at leastone cascade operating on the predetermined operable signal at the inputof the at least one cascade is substantially minimized; and one or moreoutput value detection circuits respectively operably coupled with oneor more outputs of the N gain elements.
 19. The system of claim 18,wherein said means for receiving at least one signal comprises: meansfor receiving the at least one signal from a photo-detector array. 20.The system of claim 19, wherein said means for receiving the at leastone signal from a photo-detector any comprises: means for receiving theat least one signal from at least one of a charge coupled device (CCD)array or a complementary metal oxide semiconductor (CMOS) array.
 21. Thesystem of claim 18, wherein the N greater than or equal to a positiveinteger sufficient to provide the at least one cascade with a gain suchthat a predetermined operable signal at an input of the at least onecascade generates a signal at an output of the at least one cascade thatis larger than a predetermined operable threshold value furthercomprises: the N greater than or equal to a positive integer sufficientto provide the at least one cascade with a gain such that asubstantially minimally rated output signal of a photo-detector arrayapplied to the input of the at least one cascade generates a signal atthe output of the at least one cascade that is larger than thepredetermined operable threshold value.
 22. The system of claim 18,wherein the N greater than or equal to a positive integer sufficient toprovide the at least one cascade with a gain such that a predeterminedoperable signal at an input of the at least one cascade generates asignal at an output of the at least one cascade that is larger than apredetermined operable threshold value further comprises: the N isgreater than or equal to a positive integer sufficient to provide the atleast one cascade with a gain such that a predetermined signal at aninput of the at least one cascade generates a signal at the output ofthe at least one cascade that is larger than a substantially minimallyrated input of a display circuit.
 23. The system of claim 18, whereinthe gain element of the at least one cascade having a gain larger thanone by an amount such that a noise factor of the at least one cascadeoperating on the predetermined operable signal at the input of the atleast one cascade is substantially minimized further comprises: a noisefactor defined as a ratio of a Signal Power to Thermal Noise ratio atthe input of the at least one cascade to an amplified Signal Power toThermal Noise ratio at the output of the at least one cascade:(S_(input)/N_(input))/(S_(output)/N_(output)).
 24. The system of claim18, wherein the gain element of the at least one cascade having a gainlarger than one by an amount such that a noise factor of the at leastone cascade operating on the predetermined operable signal at the inputof the at least one cascade is substantially minimized furthercomprises: a noise factor defined as a ratio of an output noise power ofthe at least one cascade to the portion thereof attributable to thermalnoise in an input termination at standard noise temperature.
 25. Thesystem of claim 18, wherein the gain element of the at least one cascadehaving a gain larger than one by an amount such that a noise factor ofthe at least one cascade operating on the predetermined operable signalat the input of the at least one cascade is substantially minimizedfurther comprises: a noise factor defined as a ratio of actual outputnoise to that which would remain if the at least one cascade itself didnot introduce noise.
 26. The system of claim 18, wherein the gainelement of the at least one cascade having a gain larger than one by anamount such that a noise factor of the at least one cascade operating onthe predetermined operable signal at the input of the at least onecascade is substantially minimized further comprises: the gain largerthan one but less than 1.001.
 27. The system of claim 18, wherein thegain element of the at least one cascade having a gain larger than oneby an amount such that a noise factor of the at least one cascadeoperating on the predetermined operable signal at the input of the atleast one cascade is substantially minimized further comprises: the gainlarger than one but less than 1.01.
 28. The system of claim 18, whereinthe gain element of the at least one cascade having a gain larger thanone by an amount such that a noise factor of the at least one cascadeoperating on the predetermined operable signal at the input of the atleast one cascade is substantially minimized further comprises: the gainof a gain element is larger than one by an amount that is practicablysmall such that the noise contribution to the low noise amplifier from again element is substantially minimized.
 29. The system of claim 18,wherein the gain element of the at least one cascade having a gainlarger than one by an amount such that a noise factor of the at leastone cascade operating on the predetermined operable signal at the inputof the at least one cascade is substantially minimized furthercomprises: an impact ionization-based amplifier having a gain largerthan one by an amount such that the noise factor of the at least onecascade operating on the predetermined operable signal at the input ofthe cascade is substantially minimized.
 30. The system of claim 18,further comprising: means for detecting that a first gain element outputof N gain elements in a cascade is below a first predefined threshold;and means for determining a digital conversion value in response to adetection that a second gain element output of the N gain elements inthe cascade is above a second predefined threshold greater than thefirst predefined threshold.
 31. The system of claim 30, wherein saidmeans for determining a digital conversion value in response to adetection that a second gain element output of the N gain elements inthe cascade is above a second predefined threshold greater than thefirst predefined threshold comprises: means for obtaining a first boundby dividing the first predefined threshold by an aggregate gain betweenthe first gain element output and a defined analog input; means forobtaining a second bound by dividing the second predefined threshold byan aggregate gain between the second gain element output and the definedanalog input; means for determining a signal value bounded by the firstbound and the second bound; and means for obtaining the digitalconversion value in response to the signal value.
 32. The system ofclaim 31, wherein said means for obtaining the digital conversion valuein response to the signal value comprises: means for designating thesignal value as the digital conversion value.
 33. The system of claim31, wherein said means for obtaining the digital conversion value inresponse to the signal value comprises: at least one of means forquantizing the signal value or means for digitizing the signal value.34. The method of claim 30, wherein said means for determining a digitalconversion value in response to a detection that a second gain elementoutput of the N gain elements in the cascade is above a secondpredefined threshold greater than the first predefined thresholdcomprises: means for receiving one or more output signals of the N gainelements with one or more comparators respectively operably coupled withthe one or more outputs of the N gain elements.